Infection of humans with miroorganisms has long been a matter of conventional concern. In particular, the risk of various infections to humans is further increasing with the development of modes of transportation and expansion of the living areas of people in recent years. Representative examples of therapeutic agents against infections include antibiotics. However, an antibiotic is a medicine that can exhibit its effects only when it inhibits the in vivo metabolic pathway of a pathogen. Nevertheless, viruses depend totally on host cells in terms of protein synthesis and energy production mechanisms and lack their own metabolic pathways. Hence, antibiotics cannot exhibit direct viral inhibitory effects. Therefore, infections caused by viruses rather than bacteria are currently becoming a threat.
Viruses are minute microorganisms having no cell structure, and they are broadly classified as DNA viruses or RNA viruses. There exist three modes of viral infection: acute infection with significant disintegration of host cells; persistent infection with clinical symptoms that remain at relatively minor levels but become chronic; and latent infection with viruses that remain in a state in which no observable viral protein synthesis takes place for a long time period, although cancer is induced in some cases.
Examples of an RNA virus causing a human disease include Japanese encephalitis virus, hepatitis C virus (HCV), and the like of the family Flaviviridae, Rotavirus and the like of the family Reoviridae, mumps virus, measles virus, and the like of the family Paramyxoviridae, influenza virus and the like of the family Orthomyxoviridae, and human immunodeficiency virus (HIV) and the like of the family Retroviridae.
Among such diseases, hepatitis C, which is caused by infection with hepatitis C virus, tends to be chronic. Once hepatitis C becomes chronic, it becomes a severe disease, with a high percentage of cases progressing to cirrhosis or liver cancer. An effective therapeutic method is strongly desired. Regarding influenza viruses, it is well known that pandemic outbreak thereof occurs every several years. It is also known that patients may die if the infection left untreated. Therefore, an urgent need is to provide the market with a remedy effective against influenza viruses.
Examples of an antiviral agent against an RNA virus include Amantadine, Zanamivir, Oseltamivir, and the like against influenza viruses, Zidovudine, Nevirapine, Ritonavir, and the like against HIV, and Ribavirin and the like against HCV.
However, currently used remedies against viral disease are still under development since they are problematic in terms of adverse reaction, effectiveness, and the like, as suggested. Also, another problem may arise such that a virus resistant to an antiviral agent considered to be effective appears. Therefore, development of a novel antiviral agent is still desired.
The present inventors have studied proteins involved in splicing regulation. In the course of this study, the present inventors have discovered that a group of compounds including compounds represented by the following formulae exhibit inhibitory activity against SRPK, which is a kinase and thus have antiviral effects, as disclosed in International Patent Publication Pamphlet WO2005/063293.
